A band pass filter is provided in a wireless communication apparatus or the like to extract high frequency signals in a desired frequency band from reception signals received by an antenna, for example. Band pass filters constituted by SAW filters are typical of the prior art. However, it is difficult to form a SAW filter in an integrated circuit, and therefore the SAW filter is provided to an integrated circuit apparatus externally as a discrete circuit element. As a result, the SAW filter causes an increase in the cost of the wireless communication apparatus.
Meanwhile, active filters and switched capacitor filters are gaining attention as on-chip filters. For example, “Japanese Patent Application Publication No. 2008-301182” “Williams & Fred Taylor, “Electronic Filter Design Handbook 4th Edition”, McGraw-Hill, page 207, Chapter 5” “S. Arnim, V. Giannini and A. Baschirotto, “A 4th Order Active-Gm-RC Reconfigurable (UMTS/WLAN) Filter”, IEEE J. Solid-State Circuit, pp. 1630-1637, 2006” “H. Kondo, M. Sawada, N. Murakami and S. Masui, “Design of Complex BPF with Automatic Digital Tuning Circuit for Low-IF Receivers”, IEICE Trans. Electron., pp. 1304-1310, 2009” and “Tien-Yu Lo, Chuan-Cheng Hsiao, Kang-Wei Hsuch, and Hung-Sung Li, “A 1-V 60 MHz Bandpass Filter with Quality-Factor Calibration in 65 nm CMOS”, Proc. Of IEEE Asia Solid-State Circuit Conference, pp. 53-56, 2009” and so on, are available.
In theory, a band pass filter can be constructed by combining a low pass filter with a high pass filter.
In “Tien-Yu Lo, Chuan-Cheng Hsiao, Kang-Wei Hsuch, and Hung-Sung Li, “A 1-V 60 MHz Bandpass Filter with Quality Factor Calibration in 65 nm CMOS”, Proc. Of IEEE Asia Solid-State Circuit Conference, pp. 53-56, 2009”, a second order band pass filter (BPF) is formed from two OTAs (Operational Transconductance Amplifiers), and accordingly, a fifth order band pass filter (BPF) is formed from ten OTAs. However, since the number of OTAs is large, a large power consumption of 23.5 mW is generated.
It is, however, not easy to reduce the power consumption of a high order band pass filter having a sharp characteristic. For example, to raise a Q value of the BPF, a unity gain frequency fu (Hz) of the OTA forming the BPF is better to be set at no less than ten times a center frequency fc of the BPF. However, the power consumption of the OTA typically increases when the unity gain frequency fu is increased. The reason for this is that to enable the OTA to operate at a high frequency, a gm (transconductance) is increased by increasing a drain current of a transistor, for example.